Passing State in Email Actions

You can pass state via a continue URL when sending email actions for password
resets or verifying a user's email. This provides the user the ability to be
returned to the app after the action is completed. In addition, you can specify
whether to handle the email action link directly from a mobile application when
it is installed instead of a web page.

This can be extremely useful in the following common scenarios:

A user, not currently logged in, may be trying to access content that
requires the user to be signed in. However, the user might have forgotten
their password and therefore trigger the reset password flow. At the end of
the flow, the user expects to go back to the section of the app they were
trying to access.

An application may only offer access to verified accounts. For
example, a newsletter app may require the user to verify their email before
subscribing. The user would go through the email verification flow and expect
to be returned to the app to complete their subscription.

In general, when a user begins a password reset or email verification flow on
an iOS app they expect to complete the flow within the app; the ability to
pass state via continue URL makes this possible.

Having the ability to pass state via a continue URL is a powerful feature that
Firebase Auth provides and which can significantly enhance the user experience.

Passing state/continue URL in email actions

In order to securely pass a continue URL, the domain for the URL will need to
be whitelisted in the Firebase console.
This is done in the Authentication section by adding this domain to the
list of Authorized domains under the Sign-in method tab if it is not already there.

A FIRActionCodeSettings instance needs to be provided when sending
a password reset email or a verification email. This interface takes the
following parameters:

Swift

Parameter

Type

Description

URL

String

Sets the link (state/continue URL) which has different meanings
in different contexts:

When the link is handled in the web action widgets, this is the deep
link in the continueUrl query parameter.

When the link is handled in the app directly, this is the
continueUrl query parameter in the deep link of the
Dynamic Link.

iOSBundleID

String

Sets the iOS bundle ID. This will try to open the link in an iOS app if
it is installed. The iOS app needs to be registered in the Console. If no
Bundle ID is provided, the value of this field is set to the bundle ID of
the App's main bundle.

androidPackageName

String

Sets the Android package name. This will try to open the link in an
android app if it is installed.

androidInstallIfNotAvailable

Bool

Specifies whether to install the Android app if the device supports it
and the app is not already installed. If this field is provided without a
packageName, an error is thrown explaining that the packageName must be
provided in conjunction with this field.

androidMinimumVersion

String

The minimum version of the app that is supported in this flow. If
minimumVersion is specified, and an older version of the app is installed,
the user is taken to the Play Store to upgrade the app. The Android app
needs to be registered in the Console.

handleCodeInApp

Bool

Whether the email action link will be opened in a mobile app or a web
link first. The default is false. When set to true, the action code link
will be be sent as a Universal Link or Android App Link and will be opened
by the app if installed. In the false case, the code will be sent to the
web widget first and then on continue will redirect to the app if
installed.

dynamicLinkDomain

String

Sets the dynamic link domain (or subdomain) to use for the current link
if it is to be opened using Firebase Dynamic Links. As multiple dynamic
link domains can be configured per project, this field provides the
ability to explicitly choose one. If none is provided, the first domain
is used by default.

Objective-C

Parameter

Type

Description

URL

NSString

Sets the link (state/continue URL) which has different meanings
in different contexts:

When the link is handled in the web action widgets, this is the deep
link in the continueUrl query parameter.

When the link is handled in the app directly, this is the
continueUrl query parameter in the deep link of the
Dynamic Link.

iOSBundleID

NSString

Sets the iOS bundle ID. This will try to open the link in an iOS app if
it is installed. The iOS app needs to be registered in the Console.

androidPackageName

NSString

Sets the Android package name. This will try to open the link in an
android app if it is installed.

androidInstallIfNotAvailable

BOOL

specifies whether to install the Android app if the device supports it
and the app is not already installed. If this field is provided without a
packageName, an error is thrown explaining that the packageName must be
provided in conjunction with this field.

androidMinimumVersion

NSString

The minimum version of the app that is supported in this flow. If
minimumVersion is specified, and an older version of the app is installed,
the user is taken to the Play Store to upgrade the app. The Android app
needs to be registered in the Console.

handleCodeInApp

BOOL

Whether the email action link will be opened in a mobile app or a web
link first. The default is false. When set to true, the action code link
will be be sent as a Universal Link or Android App Link and will be opened
by the app if installed. In the false case, the code will be sent to the
web widget first and then on continue will redirect to the app if
installed.

dynamicLinkDomain

NSString

Sets the dynamic link domain (or subdomain) to use for the current link
if it is to be opened using Firebase Dynamic Links. As multiple dynamic
link domains can be configured per project, this field provides the
ability to explicitly choose one. If none is provided, the first domain
is used by default.

The following example illustrates how to send an email verification link that
will open in a mobile app first as a Firebase Dynamic Link using the custom
dynamic link domain example.page.link
(iOS app com.example.ios or Android app com.example.android where the app
will install if not already installed and the minimum version is 12). The
deep link will contain the continue URL payload
https://www.example.com/?email=user@example.com.

Configuring Firebase Dynamic Links

Firebase Auth uses Firebase Dynamic Links when sending a
link that is meant to be opened in a mobile application. In order to use this
feature, Dynamic Links need to be configured in the Firebase Console.

If you have not yet accepted the Dynamic Links terms and created a Dynamic Links
domain, do so now.

If you already created a Dynamic Links domain, take note of it. A Dynamic Links
domain typically looks like the following example:

example.page.link

You will need this value when you configure your iOS or Android app to
intercept the incoming link.

Configuring Android applications:

If you plan on handling these links from your Android appliction, the
Android package name needs to be specified in the Firebase Console
project settings. In addition, the SHA-1 and SHA-256 of the application
certificate need to be provided.

You will also need to configure the intent filter for the deep link in
you AndroidManifest.xml file.

If you plan on handling these links from your iOS appliction, the
iOS bundle ID needs to be specified in the Firebase Console
project settings. In addition, the App Store ID and the Apple Developer
Team ID also need to be specified.

You will also need to configure the FDL universal link domain as an
Associated Domain in your application capabilities.

If you plan to distribute your application to iOS versions 8 and under,
you will need to set your iOS bundle ID as a custom scheme for incoming
URLs.

Handling email actions in a web application

You can specify whether you want to handle the action code link from a web
application first and then redirect to another web page or mobile application
after successful completion, provided the mobile application is available.
This is done by setting handleCodeInApp to false in the
FIRActionCodeSettings (Obj-C) or ActionCodeSettings (Swift) object. While
an iOS bundle ID
or Android package name are not required, providing them will allow the user
to redirect back to the specified app on email action code completion.

The web URL used here, is the one configured in the email action templates
section. A default one is provisioned for all projects. Refer to
customizing email handlers to learn more on
how to customize the email action handler.

In this case, the link within the continueURL query parameter will be
an FDL link whose payload is the URL specified in the ActionCodeSettings
object. While you can intercept and handle the incoming link from your app
without any additional dependency, we recommend using the FDL client library to
parse the deep link for you.

When handling email actions such as email verification, the action code from the
oobCode query parameter needs to be parsed from the deep link and then applied
via applyActionCode for the change to take effect, i.e. email to be verified.

Handling email actions in a mobile application

You can specify whether you want to handle the action code link within your
mobile application first, provided it is installed. With Android applications,
you also have the ability to specify via the androidInstallIfNotAvailable that
the app is to be installed if the device supports it and it is not already
installed.
If the link is clicked from a device that does not support the mobile
application, it is opened from a web page instead.
This is done by setting handleCodeInApp to true in the
FIRActionCodeSettings (Obj-C) or ActionCodeSettings (Swift) object. The
mobile application's Android package name or iOS bundle ID will also need to be
specified.The fallback web URL used here, when no mobile app is available, is
the one configured in the email action templates section. A default one is
provisioned for all projects. Refer to
customizing email handlers to learn more on
how to customize the email action handler.

In this case, the mobile app link sent to the user will be an FDL link whose
payload is the action code URL, configured in the Console, with the query
parameters oobCode, mode, apiKey and continueUrl. The latter will be the
original URL specified in the FIRActionCodeSettings (Obj-C) or
ActionCodeSettings (Swift) object. While you can intercept and handle the
incoming link from your app without any additional dependency, we recommend
using the FDL client library to parse the deep link for you. The action code can
be applied directly from a mobile application similar to how it is handled from
the web flow described in the
customizing email handlers section.

When handling email actions such as email verification, the action code from the
oobCode query parameter needs to be parsed from the deep link and then applied
via applyActionCode for the change to take effect, i.e. email to be verified.